Grinding wheel

ABSTRACT

The invention relates to a grinding wheel for machining metal circular-saw blades at relatively high rotational speeds, which have machining areas which contain in particular hard materials, such as for example diamond or cubic boron nitride. The grinding wheels according to the invention are intended in particular to improve the centring at relatively high rotational speeds, and consequently to prevent true running problems as far as possible. The base body of the grinding wheel is of contoured design, at least on one side, in the radially outer area of a tool-mounting bore, and at least one centring element can be designed to engage in a formfitting manner in the correspondingly designed contours, so that the grinding wheel and a centring element on a tool spindle of a grinding machine are held together in a force-fitting manner.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a U.S. national application of internationalapplication Serial No. PCT/DE98/00484 filed Feb. 17, 1998, which claimspriority to German Serial Nos. 197 19 971.2 and 297 15 683.7 filed May13, 1997 and Sep. 1, 1997, respectively.

The invention relates to a grinding wheel for machining metal-circularsaw blades at relatively high rotational speeds, such grinding wheelshaving machining areas which contain hard materials, such as for examplediamond or cubic boron nitride, which can be used to achieve highmaterial-removal rates.

DE 296 08 590 has disclosed grinding wheels for machining metalcircular-saw blades, in which the centering and alignment on a driveshaft of a grinding machine is intended to be improved by designing thediameter of the tool-mounting bore which is formed in the grinding wheelto widen on one side.

However, grinding wheels whose machining areas contain cubic boronnitride or diamond abrasive particles allow very high material-removalrates to be achieved if the cutting rate and therefore the rotationalspeed of the grinding wheel are set to be correspondingly higher. Theseincreased rotational speeds lead to the centering, which the design ofthe tool-mounting bore is supposed to improve, deteriorating as a resultof the increasing centrifugal forces.

Furthermore, this leads to true running problems arising, and inparticular to the vibrations, which are transmitted into the machiningarea by the true running problems, causing high levels of wear in themachining area as a result of increased abrasion of the hard materials,so that the grinding wheels have to be dressed or replaced morefrequently.

Therefore, the object of the invention is to improve grinding wheels insuch a manner that the centering can be improved, in particular atrelatively high rotational speeds, and consequently true runningproblems can be avoided.

According to the invention, this object is achieved by means of thefeatures of claim 1. Advantageous configurations and refinements of theinvention are given by using the features mentioned in the subordinateclaims.

The grinding wheels according to the invention differ from the grindingwheels which have customarily been used hitherto in particular in that acontour, in which at least one centering element can engage in aform-fitting manner, is provided in the base body of the grinding wheel,at least on one side, in the radially outer region of the tool-mountingbore, which may be of conventional design or may be designed asdisclosed by DE 296 08 590. During grinding, the grinding wheel and atleast one centering element are held in a force-fitting manner on thetool spindle of the grinding machine. For this purpose, a conventionalscrew connection, for example, may be used, although it is also possibleto employ hydraulically or pneumatically actuable piston-cylinder unitsor a spring force, these options being suitable in particular forautomatic operation.

It is particularly advantageous for the contour to be formed on bothsides of the base body of the grinding wheel, and to maintainsymmetrical conditions.

The only factor which needs to be taken into account during contouringis that a bearing surface for the centering element(s) is to be presenton at least one side, on which bearing surface a surface, which isdirected towards the axis of rotation of the grinding wheel, of thecentering element(s) is supported, and the centering action can beimproved at relatively high rotational speeds as a result of thecentrifugal forces.

There are a number of possible designs for the contour(s). A circulargroove may be formed on one or both sides of the base body of thegrinding wheel, in which groove corresponding webs on the centeringelement(s) engage in a form-fitting manner and virtually without playwhen the grinding wheel is attached to the drive spindle of the grindingmachine. It is advantageous if those areas of the centering element(s)which engage in the grooves and are of web-like design are convex, atleast on their internal diameter, so that they do not bear against thecorresponding surface of the groove over the entire area, thusfacilitating insertion.

Another possible design of the contour(s) consists in forming aflange-like widening, which projects beyond the normal thickness of thebase body of the grinding wheel and on which there is at least oneradially outer bearing surface for the centering element (s), on whichbearing surface the centering element(s) can be supported.Advantageously, the bearing surface(s) is/are inclined with respect tothe axis of rotation.

The contour may also, however, be a web which runs in a circle and may,if appropriate, be symmetrically divided into individual segments bymeans of apertures. In this case, the centering element(s) is/are ineach case supported against the radially outer surface of the web.

The possible examples for the design of the contours may be improved byforming bearing surfaces which are bevelled on at least one side and onwhich the corresponding bearing surfaces on the centering element(s) aresupported. Bevelled surfaces have the advantage, on the one hand, ofproviding larger bearing surfaces and, on the other hand, offacilitating the introduction or fitting together of the centeringelements when the grinding wheel is being attached to the grindingmachine, and if necessary alignment errors can be compensated for duringintroduction, thus reducing the wear on the centering elements and thebase body of the grinding wheel.

The possible designs of the contours which have been described thus farcan be achieved relatively easily by machining operations for the caseof the grooves and the flange-like design, but it is also possible toprovide the base body of the grinding wheel with the desired shape bymeans of known casting processes.

Furthermore, it is also possible to achieve the improvement in thecentering for the grinding wheels in question by designing the contoursin the form of apertures or recesses through or in the base body of thegrinding wheel, or by additionally providing such recesses or apertures.In this case, at least two apertures or recesses which are arrangedsymmetrically opposite one another in the radial direction on one axisare required, in order to compensate for the centrifugal forces whicharise and to avoid undesirable imbalances.

The recesses or apertures may advantageously be improved if they aredesigned to widen conically outwards, in order, as is already the casefor the bevelled design of certain surface areas of the grooves, flangesor webs, to improve in particular the insertion of the centeringelements.

It is advantageous for one of the corresponding centering elements to beprovided in a stationary position on the flange of the drive spindle ofthe grinding machine, while on the other side of the grinding wheel anadditional centering element, which is preferably of correspondingdesign, is held in a force-fitting manner in the contour and thetool-mounting bore of the grinding wheel. The second centering elementmay in this case be a separate component which can be held in aforce-fitting manner towards the flange of the drive spindle of thegrinding machine.

If the grinding wheel is attached to the drive spindle by means of ascrew connection, it is advantageous to join the screw and the centeringelement together, thus facilitating handling. It is particularlyadvantageous if the connection is designed in such a way that the screwcan rotate independently of the movement of the centering element, i.e.in such a manner that the centering element is prevented from rotatingwith the screw.

If, on the other hand, a piston-cylinder arrangement is selected, thecentering element may be part of the piston or of the cylinder,depending on which of the two elements is used to attach the grindingwheel to the drive spindle.

In addition to the improved centering action at high rotational speeds,which is improved by the improved support for the grinding wheel in theradial direction, and is further promoted by the centrifugal forceeffect, noting that the centrifugal force increases as the square of thespeed, it is also possible to transmit a higher torque as a result ofincreasing the sizes of the surfaces which are frictionally connected.

The invention will be explained in more detail below with reference toexemplary embodiments. In the drawings:

FIG. 1 shows a number of possible designs for a grinding wheel accordingto the invention;

FIG. 2 shows an example of a grinding wheel according to the inventionon its own, and

FIG. 3 shows the example illustrated in FIG. 2, in a centering, securedposition.

FIG. 1 shows a number of possible contours which can be used accordingto the invention.

Contours in the form of webs 2 and 2′ are shown on the grinding wheel 1above the axis of rotation A, the web 2 to the right of the center axisB of the grinding wheel 1 being virtually symmetrical, with arectangular or square cross-section; this design can be produced atlower cost, at least if the corresponding base body of a grinding wheel1 is machined, than the web 2′ which is shown to the left of the centeraxis B and which has at least one bevelled or convex bearing surface fora centering element. In the example shown, the radially inner bearingsurface of the web 2′ is bevelled, although it is also possible for theradially outer bearing surface of this web, or even both bearingsurfaces, to be of bevelled or convex design.

Contours in the form of grooves 3 and 3′ are shown below the axis ofrotation A, a groove 3 of rectangular or square cross-section againbeing shown to the right of the center axis B of the grinding wheel 1,while the groove 3′ shown on the other side of the center axis B is tohave at least one bevelled bearing surface for a centering element (notshown).

The design of the contouring in the radially outer area of thetool-mounting bore 4, which beneath the axis of rotation A is in simpleform and above the axis of rotation A is in bevelled form, as is knownfrom DE 296 08 590, should, however, always be symmetrical with regardto the axes A and B, i.e. contours in the form of webs 2 or 2′ orgrooves 3 or 3′ should be provided on a grinding wheel 1, in order tofacilitate balancing of the grinding wheel 1.

In a similar fashion to the grooves 3 or 3′, it is also possible to formrecesses or apertures in the base body of the grinding wheel, but theserecesses or apertures should be arranged in mutually opposite pairs, andcorrespondingly projecting areas of the centering elements could engagein these recesses or apertures.

FIG. 1 furthermore shows various possible designs of the machining areas5 and 3′ of a grinding wheel according to the invention, which containthe hard materials cubic boron nitride or diamond.

FIG. 2 shows a further example of the grinding wheel 1 according to theinvention. In this case, the contour 7 is a flange-like widening in theradially outer area with respect to the tool-mounting bore 4, on theradially outer edge of which widening there are bearing surfaces 8 forone or two centering elements 6 (not shown). The bearing surfaces 8 areinclined at an angle of 15° with respect to the axis of rotation A.

Part of the internal diameter of the tool-mounting bore 4 is designed towiden conically, the cone in this case forming an angle of 90°. The coneis advantageously dimensioned in such a way that it extends at least asfar as the center axis B of the grinding-wheel base body or even beyond,while the remaining part of the tool-mounting bore 4 is of cylindricaldesign.

The tool-mounting bore 4 may, however, also be designed in such a way(not shown) that the conical part is surrounded by two cylindricalparts, in which case the cylindrical part which adjoins the largerdiameter of the conical part has a larger internal diameter than theother, opposite cylindrical part. The centering element 6 may then be ofcorresponding design and may bear against the cone and the adjoining endface of the cylindrical part of the tool-mounting bore 4.

Moreover, planar support surfaces 9 are present in the radially outerarea with respect to the tool-mounting bore 4, against which supportsurfaces the centering element(s) (6) or a clamping element bear(s) inthe fixed position of the grinding wheel 1.

The cone may, however, also be designed (in a form which is notillustrated) on both sides of the grinding wheel 1, in which case twocorrespondingly designed centering elements may be used on either side.

FIG. 3 shows the example in accordance with FIG. 2 in the position whereit has been fixed on a drive spindle of a grinding machine for metalcircular-saw blades.

A centering element 6 is connected to the drive shaft of the grindingmachine. The grinding wheel 1 is held in a force-fitting manner againstthe centering element 6 by means of a clamping screw 10, and during theattachment the grinding wheel 1 is simultaneously centered and fixed.FIG. 3 clearly shows how the conical internal diameter of thetool-mounting bore, the support surface 9 and the bearing surface 8 ofthe flange-like contour 7 of the grinding wheel 1 bear against thecentering element 6 and thus the grinding wheel 1 is held aligned. Thelarge surface areas provide reliable guidance even at relatively highrotational speeds. Moreover, relatively high frictional forces areavailable and make it possible to reduce the clamping force which has tobe applied by means of the clamping screw 10 or some other clampingelement, so that the service life of at least the centering elements 6is prolonged.

The centrifugal forces which act at high rotational speeds are absorbedand largely compensated for at the bearing surface 8 of the contour 7,with the corresponding design of the centering element 6, at the outeredge of the latter. For this purpose, the centering element 6 isrecessed between its outer edge and the conically widening externaldiameter, i.e. in the area of the support surface 9 which is present onthis side of the grinding wheel 9 and is smaller than the supportsurface 9 which is present on the other side. As a result, the innerouter edge of the centering element 6 bears against the bearing surface8, and the recessed area bears against the support surface 9.

What is claimed is:
 1. A grinding wheel for centrally mounting on a toolfor machining metal circular-saw blades, the grinding wheel comprising aradially outer area having a machining area which is provided with anabrasive coating, a center mount area including a tool-mounting borewith an internal diameter which widens on at least one side of thegrinding wheel (1), further including a base body having on at least oneside a contour in the radially outer region of the center mount area(4), for the form-fitting engagement of a centering element (6) havingan external contour, the external contour being matched to the internalcontour of the center mount area (4), wherein the contour (7) is aflange-like widening greater in thickness than the grinding-wheel basebody, the widening having at least one radially outer bearing surface(8) for engaging the centering element (6), and further including planarsupport surfaces (9) positioned perpendicular to the axis of rotation(A) between the at least one bearing surface (8) and the center mountarea (4).
 2. The grinding wheel according to claim 1 wherein the contouris formed on both sides of the grinding wheel (1).
 3. The grinding wheelaccording to claim 1 wherein the contour (7) is a flange-like wideningbeyond the thickness of the grinding-wheel base body, which widening hasat least one radially outer bearing surface (8) for a centering element(6).
 4. The grinding wheel according to claim 1 wherein the at least onebearing surface (8) is bevelled with respect to the axis of rotation (A)of the grinding wheel (1).
 5. The grinding wheel according to claim 3further including planar support surfaces (9) which are perpendicular tothe axis of rotation (A), the planar support surfaces being providedbetween the bearing surface(s) (8) and tool-mounting bore (4).
 6. Thegrinding wheel according to claim 1 wherein the contour is a circularweb.
 7. The grinding wheel according to claim 1 further including atleast two apertures or recesses which lie symmetrically opposite oneanother in the radial direction on a single axis, the at least twoapertures being formed in the base body of the grinding wheel (1). 8.The grinding wheel according to claim 7 wherein the recesses orapertures widen conically outwards.
 9. The grinding wheel according toclaim 1 wherein the tool-mounting bore (4) includes a tapering partwhich tapers from one side of the grinding wheel (1), and the remainingpart of the tool-mounting bore (4) is cylindrical.
 10. The grindingwheel according to claim 9 wherein the tapering part of thetool-mounting bore (4) extends at least as far as a center of thegrinding-wheel base body.
 11. The grinding wheel according to claim 9wherein the tapering part of the tool-mounting bore (4) is surrounded onboth sides by cylindrical parts having different internal diameters. 12.The grinding wheel according to claim 9 wherein the tapering parts ofthe tool-mounting bore (4) and of the centering element (6) are formedat an angle of 90°.
 13. A grinding wheel for machining metalcircular-saw blades, which at least in its radially outer area has amachining area which is provided with an abrasive coating and, in thearea of the tool-mounting bore, is designed with an internal diameterwhich widens on at least one side wherein the base body of the grindingwheel (1), at least on one side, has an additional contour (2, 2′, 3,3′, 7) in the radially outer region of the tool-mounting bore (4), forthe form-fitting engagement of a centering element (6), the externalcontour of which is matched to the internal contour of the tool-mountingbore (4), the contour (7) is a flange-like widening beyond the thicknessof the grinding-wheel base body, which widening has at least oneradially outer bearing surface (8) for a centering element (6), the atleast one bearing surface (8) is bevelled with respect to the axis ofrotation (A) of the grinding wheel (1), the bearing surfaces (8) beinginclined at an angle of 15° with respect to the axis of rotation (A) ofthe grinding wheel (1).